Select the incorrect pair:

Two blocks of masses $1 \ kg$ and $2 \ kg$ are connected by a metal wire going over a smooth pulley. The breaking stress of the metal is $\frac{40}{3 \pi} \times 10^6 \ N m^{-2}$. What should be the minimum radius of the wire used if it should not break (in $mm$)? $\left(g = 10 \ m s^{-2}\right)$

$A$ diatomic gas $\left(\gamma = \frac{7}{5}\right)$ is compressed adiabatically to a volume $\frac{V_i}{32}$,where $V_i$ is its initial volume. The initial temperature of the gas is $T_i$ in Kelvin and the final temperature is $xT_i$. The value of $x$ is:

$\int_0^\pi \frac{x \tan x}{\sec x+\tan x} d x=$

The electronic configurations of $Cr^{2+}, Mn^{2+}, Fe^{2+},$ and $Ni^{2+}$ are $3d^4, 3d^5, 3d^6,$ and $3d^8$ respectively. Which one of the following aqua complexes will exhibit the minimum paramagnetic behavior?

The velocity at the mean position of a particle executing $S.H.M.$ is $v$. What is the velocity of the particle at a distance equal to half of the amplitude?